This invention relates to drill string sections comprising internal passages that facilitate the electrical or hydraulic connection of multiple devices, such as sensors, arranged at spaced apart positions along the length of the drill sections. This invention also relates to methods of manufacturing drill sections comprising internal passages.
Drilling assemblies for boring holes deep into the earth are well known. For example, drilling assemblies are used by the oil and gas industry for retrieving various fluids and gases buried within earth formations. Typical drilling assemblies comprise a drilling string including a plurality of interconnected sections with a drill bit on the end thereof. Rotating the interconnected sections may rotate the drill bit. Alternatively, the interconnected sections are held static and the drill bit rotated by employing internally disposed mechanisms that are driven by drilling fluid commonly referred to as xe2x80x9cmud,xe2x80x9d which is supplied under pressure from a surface source into the drill string. The drilling fluid discharges at the drill bit and returns to the surface through the annular space between the drill string and the wellbore wall. Fluid returning to the surface may carry cuttings produced by the drill bit, as well as, conditions of the formation being cut and the condition of the drill bit itself.
Down hole measuring and communication systems frequently referred to as measurement-while-drilling (xe2x80x9cMWDxe2x80x9d) and logging-while drilling (xe2x80x9cLWDxe2x80x9d) are typically disposed within drill string sections above and in close proximity to the drill bit. The systems comprise sensors for collecting down hole parameters, such as parameters concerning the drilling assembly itself, the drilling fluid, and those of formations surrounding the drilling assembly. For example, sensors may be employed to measure the location and orientation of the drill bit, and to detect buried utilities and other objections, critical information in the underground utility construction industry. Sensors may be provided to determine the density, viscosity, flow rate, pressure and temperature of the drilling fluid. Other sensors are used to determine the electrical, mechanical, acoustic and nuclear properties of the subsurface formations being drilled. Chemical detection sensors may be employed for detecting the presence of gas. These measuring and communication systems may further comprise power supplies and microprocessors that are capable of manipulating raw data measured by the various sensors. Information collected by sensors may be stored for later retrieval, transmitted to the earth""s surface via telemetry while drilling, or both. Transmitted information provides the bases for adjusting the drilling fluid properties and/or drilling operation variables, such as drill bit speed and direction.
A drill string section including an MWD and/or LWD system will generally have several sensors positioned at spaced apart locations along the length of the drill string, a microprocessor, and a power supply, all being electrically connected by wires. In other applications, such as, for example, pressure sensors, it is desirable to connect spaced apart locations (along a drill collar) hydraulically by fluid passages.
Normally passages are drilled from the ends of the drill string section to house the electrical wires, and thereafter sealed in some manner, such as by welding. The ends of drill string sections usually comprise a coupling means, commonly a threaded portion, such that a plurality of drill sting sections can be directly interconnected without employing additional hardware. Unfortunately, the presence of the passages within a threaded end region creates stress risers that may lead to structural failure of the drill string section. Passages within the threaded ends also create problems for threading re-work, which is beneficial for extending the life of a drill string section.
One solution to the above-identified problems that has been used in the past is to drill passages from one end of a first drill pipe and towards its opposing end, seal the passage opening, and then weld a second drill pipe that does not contain any passages to the sealed end of the first drill pipe. A threaded connection can then be formed on the exposed ends of the connected drill pipes, thereby maintaining the passage internally and distal to the threaded connections.
This drill string section manufacturing technique, however, has limitations. The first drill pipe comprising the wire passage will generally have relatively thicker walls (that is, a relatively smaller bore) to accommodate the wire passage, whereas the second drill pipe will have relatively thinner walls (that is, a larger relative bore) to minimize weight and manufacturing cost while maximizing flow rates of drilling fluid. In such a stepped bore arrangement the weld joint is necessarily located, at least partially, in a thin-walled area (interface of the connected first and second drill pipes). This can compromise the structurally integrity of the resulting drill string section, and limit the maximum strain the drill string section can tolerate before failure.
Another limitation of this manufacturing technique is the length of the drill string section and number of sensors accomodatable therewith. It is preferred to have drill string sections as long as possible to improve drilling efficiency, and to employ several sensors and corresponding electrical devices. Since the wire passage is only formed in the first section of drill pipe, the overall length of the drill string section will be limited to that of current methods of small diameter and long hole drilling.
Accordingly, a need still exists for improved methods of manufacturing drill string sections that comprise lengthy internal wire passages, and that overcome problems such as those described above.
The present invention provides an improved method of manufacturing a drill string section comprising an internal passage. In accordance with a preferred embodiment of the present invention, there has now been provided a method of manufacturing a drill string section including an internal passage extending along a substantial portion of its length, the method comprising the steps of: providing a drill string section comprising a first end, an opposing second end, an outer surface, and a centrally disposed bore extending from the first end to the second end so as to form a wall between the bore and the outer surface; separating the drill string section into first and second portions, the first portion comprising the first end and a third end formed by said separation, the second portion comprising the second end and a fourth end formed by said separation; forming a first blind and generally axially extending passage through the wall from the third end towards the first end and to a position spaced apart from the first end; forming a second blind and generally axially extending passage through the wall from the fourth end towards the second end and to position spaced apart from the second end; joining the third end of the first portion to the fourth end of the second portion so as to form a unitary section of drill string in which the first and second passages are misaligned; and forming a connecting passage from the outer surface of the drill string section that intersects the first and second passages, whereby the connected first and second passages define the drill sting section internal passage.
In accordance with another embodiment of the present invention, there has now been provided a method of manufacturing a drill string section including an internal passage extending along a substantial portion of its length, the method comprising the steps of: providing first and second drill pipes, each pipe comprising a first end, an opposing second end, a pipe wall, and a passage extending generally axially through the pipe wall from the first end to a position spaced apart from the second end; joining the first and second drill pipes at their respective first ends so that the passages are misaligned and so as to form the drill string section; and forming a connecting passage from an outer surface of the drill string section that intersects the two passages, whereby the connected two passages define the drill string section internal passage.
The present invention also provides a drill string section including an internal passage extending along a substantial portion of its length. Drill string section embodiments provided by the present invention can be made by methods such as those described above and provided by the present invention, but are not limited thereto. In accordance with a preferred embodiment, there has now been provided a drill string section comprising a first end; a second end; a wall; an intermediate weld joint; a first blind and generally axially extending passage extending through the wall from the weld joint toward the first end; a second blind and generally axially extending passage extending through the wall from the weld joint toward the second end, the second passage being misaligned with the first passage; and a connecting passage extending through the weld joint intersecting the first and second passages, the connecting passage oriented at an acute angle with respect to a drill string section centerline; wherein the first passage, the second passage and a portion of the connecting passage define the drill string section internal passage.